Even the "harder ones" are not bad... use the rule of 45 (each line adds to 45) - and then there are a few numbers that have only one combo of numbers: a two-box of 4 can only be 3+1 etc. and a three-box of 7 can only be 1+2+4 etc... if you get all those done, then make yourself a two-combo chart of all numbers up to 17, then you can whiz through most of the puzzles.